The present invention relates to a composite on the surface of a substrate, and methods for producing the composite. More particularly, the composite includes a first coating, reflective beads, and a clear coating. More particularly, the method for preparing the composite includes the stepwise application of a first coating composition, reflective beads, and a clear coating composition.
Traffic marking coatings are one type of coating application for which reflectance and durability are particularly desirable. Traffic marking coatings are, for example, applied to roads, parking lots, and school playgrounds, the surfaces of which are typically concrete and asphalt. The resultant traffic markings instruct users and demarcate traffic lanes, parking spaces, and other restricted areas. As the replacement of solvent-borne paints continues in order to minimize air pollution, aqueous traffic marking compositions having a useful combination of dried film properties have been sought. Herein, the terms xe2x80x9ctraffic markingxe2x80x9d and xe2x80x9ctraffic marking coatingxe2x80x9d are used interchangeably.
One of the most important properties of traffic markings is the level of retroreflectance provided by the markings to enhance nighttime visibility. Retroreflectance in a traffic marking is often provided by dropping or spraying reflective beads, usually glass beads, onto the freshly applied first coating. Such beads are thought to partially sink into the first coating, and partially remain above the surface of the first coating. Light from a vehicle""s headlights is thought to strike the portion of the reflective bead protruding above the surface of the first coating, and to be reflected back toward the vehicle. Presently, traffic markings made from aqueous paints consist solely of the aqueous paint and the reflective beads. It is generally required that a traffic marking meet or exceed a minimum level of retroreflectance to be acceptable. While it is generally possible to achieve this minimum level of retroreflectance when the traffic marking is new, rapid diminution of retroreflectance with time is observed. This diminution occurs because the reflective beads tend to dislodge from the surface of the traffic marking as that surface is subjected to wear from, for example, the tires of automobiles and trucks. It is the object of the present invention to increase the durability of traffic markings by providing a new type of traffic marking which is more resistant to loss of reflective beads, and to loss of the retroreflectance they provide, when compared with current traffic markings.
U.S. Pat. No. 5,947,632 describes the use of reflective beads in traffic coatings. While the method described provides a retroreflective coating, that coating is vulnerable to rapid diminution of retroreflective properties due to abrasion of exposed surfaces of the reflective beads and due to dislodging of those beads from the coating.
U.S. Pat. Nos. 5,356,670, 5,719,237, and 5,726,244 disclose clear coatings that may be applied over pigmented coatings to enhance such characteristics as gloss and wear resistance. Unfortunately, these coating systems, which do not include reflective beads, require a curing step at high temperature during preparation. The required curing temperatures of at least 60xc2x0 C., are not feasible for many applications, especially those involving the formation of traffic markings upon road surfaces.
I have, surprisingly, found that it is possible to prepare a wear-resistant retroreflective composite having a clear coating that prevents damage to and loss of the retroreflective beads, yet allows light from, for example, an approaching vehicle to impinge upon those beads and reflect backward toward the vehicle unimpeded. These wear-resistant retroreflective composities may be prepared on road surfaces as traffic markings.
The present invention relates to a composite on a surface of a substrate, wherein the composite includes:
a) a first coating including pigment and binder polymer;
b) reflective beads; and
c) a clear coating, including binder polymer.
The present invention also relates to a method for preparing a composite on a surface of a substrate, the method including the sequential steps of:
1) applying at least one first coating composition, including pigment, binder polymer, and water, to the surface;
2) applying at least one clear coating composition, including binder polymer and water, to the surface to which the first coating composition has been applied;
3) applying reflective beads simultaneously, or nearly simultaneously, with at least one of steps 1 or 2; and
4) allowing the composite to dry.
The present invention also relates to a method for preparing a composite on a surface of a substrate, the method including the sequential steps of:
1) applying at least one first coating composition, including pigment, binder polymer, and water, to the surface;
2) applying at least one clear coating composition, including binder polymer and water, to the surface to which the first coating composition has been applied;
3) applying reflective beads in at least one step between any two consecutive steps; and
4) allowing the composite to dry.
In an aspect of the present invention, the reflective beads are spherical, or approximately spherical glass beads.
In another aspect of the present invention, the composite includes at least one absorber,
wherein the absorber is selected from the group consisting of organic super absorbent polymers, ion-exchange resins, hollow sphere polymers, molecular sieves, talcs, inorganic absorbers, porous carbonaceous materials, non-porous carbonaceous materials, and mixtures thereof.
In a still further aspect of the present invention, the surface of the substrate is a road surface, and the composite is a traffic marking.